Articles such as infant diapers, adult continence diapers, feminine napkins and the like have been manufactured generally by processes where discrete parts or components of the article are deposited on a continuously moving product web. Often, the speed with which the parts or components are produced and fed into the process is not the same as the speed of advance of the product web itself. In such cases, the speed of production and/or deposition of the component parts on the moving web must be varied to match the speed of the product web to properly match the parts to the moving web without adversely affecting the process or the quality of the finished article.
Several methods for changing the speed of a part or component of material for deposition on a continuously moving web are known in the art. One method, disclosed in U.S. Pat. Nos. 4,726,876 and 4,767,487 to Tomsovic, Jr. employs rollers segmented into sections which are inwardly and outwardly moveable in a direction radial to their direction of rotation. As the roller rotates, the segments are driven by cam actuating or gearing means to move inwardly and outwardly changing the linear surface speed of the roller segments as the roller rotates through each revolution.
U.S. Pat. No. 5,021,111 to Swenson discloses an apparatus in which an advancing web of material is fed from a slow moving feed roll to a faster moving roller which slips against the web. As components are cut from the slower moving web they are free to move with the faster moving "slip" roller from which they are then transferred to a web moving at the same speed.
Another method utilizes festoons to reduce the speed of the moving web to which the parts or components are to be applied. The continuously moving web is temporarily slowed to the speed of the component parts to be deposited, with the excess portion of the continuously moving web gathering in festoons. While the continuously moving web is slowed to match the speed of the component parts, the parts are transferred to the web and the speed of the web is then accelerated to gather the festoons prior to the next cycle.
Another method disclosed, for example, in U.S. Pat. No. 5,556,504 to Rajala, et al. employs independent segments of a cylindrical surface which comprise a portion of an arc of the circumference of the cylindrical surface. The individual segments are attached to separate concentric shafts and are free to move independently. Each arc surface moves, for a fraction of each rotation, at one speed to receive a workpiece component and then accelerates forward through an angle of rotation to transfer the component to a faster moving web.
U.S. Pat. No. 5,415,716 discloses a machine in which a first web of material is fed from a slower moving feed roller through a system of dancer rollers to a pair of pinch rollers which move the web at a faster speed.
The use of electronically controlled servomotors to control and vary the velocity of various machine roller components is known in the label-making art as illustrated, for example, in U.S. Pat. Nos. 5,380,381 and 5,413,651 to Otruba. Several patents have suggested the use of servomotors for controlling the speed of rollers in machines employed in the fabrication of infant and adult incontinence diapers, feminine care products, and the like. However, the implementation of such a suggestion has faced a number of drawbacks.
Generally, the mass of rollers required in machines for fabricating such articles presents obstacles to the use of servomotors as the driving means. The rapid acceleration/deceleration of massive rollers is beyond the long-term capability of commercially available servomotors. As a result, it has been typical in prior art machines to use mechanical means such as those described above or variable gearing arrangements to meet the demands of the heavy duty cycle imposed by massive machine rollers.
The use of servomotor drive means is also problematic when ultrasonic bonding is used as the means for bonding the discreet components to the moving web. Ultrasonic bonding is a preferable form of bonding components of diapers and feminine care products because it avoids the use of chemical adhesives with their attendant machine drawbacks. However, in machines employing ultrasonic bonding the anvil opposing the ultrasonic horn must be of a mass equal to or greater than the mass of the horn itself to prevent the resonant coupling of the anvil to the horn. This generally imposes a lower limit on the mass of anvil rollers which can be employed with ultrasonic bonding.
Typically in machines in which ultrasonic bonding is employed, the bonding horn(s) and its (their) opposed anvils are placed downstream from the rollers which cut the discrete workpiece components and mate them to the advancing web. This solves one problem, but introduces a second. The mass of the cutting and placing rollers can be lowered to enable driving the rollers by a servomotor, but the separation of the cutting and placing steps from the bonding step becomes problematic. In circumstances where the placement of workpiece components on the advancing web must be maintained with precision, any movement of the component between the placing and bonding steps leads to unacceptable product.
There is thus a need in the industry for a machine and process for cutting, and placing workpiece components from a web moving at one speed onto a receiving web moving at a different speed which permits the integration of the desirable aspects of servomotor control of machine components, while providing for precise registration and ultrasonic bonding of workpiece components.